An LED drive circuit has been known that (i) supplies a constant current to an LED by use of a DC-to-DC converter and (ii) carries out light control of the LED by changing a value of the constant current. As a method for supplying a constant current to an LED, a method is known in which an output current is detected by use of a resistor etc. and carries out voltage feedback so that the LED receives a desired current (see, for example, Patent Literature 1). However, this method will cause a problem that flickering occurs typically in a light control region of not more than 10%.
In order to avoid the problem, a method is known in which a converter such as a buck converter or a buck-boost converter is used and carries out light control by PWM (Pulse-Width Modulation) light control (see, for example, Patent Literature 2).